diff --git a/src/test/java/StockTest.java b/src/test/java/StockTest.java
index fcc0d09..6a6a477 100644
--- a/src/test/java/StockTest.java
+++ b/src/test/java/StockTest.java
@@ -1,3 +1,4 @@
+import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
 import Model.Stock;
@@ -5,35 +6,159 @@
 import static org.junit.jupiter.api.Assertions.*;
 
 import java.math.BigDecimal;
-
+import java.util.List;
 
 public class StockTest {
 
-    @Test 
-    public void testGetSalesPrice() {
-        Stock stock = new Stock("AAPL", "APPLE", new BigDecimal("1000"));
+    private Stock stock;
+
+    @BeforeEach
+    void setUp() {
+        stock = new Stock("AAPL", "Apple", new BigDecimal("1000"));
+    }
+
+    // ---- Positive tests ----
+
+    @Test
+    void testGetSymbol() {
+        assertEquals("AAPL", stock.getSymbol());
+    }
+
+    @Test
+    void testGetCompany() {
+        assertEquals("Apple", stock.getCompany());
+    }
+
+    @Test
+    void testGetSalesPrice() {
         assertEquals(new BigDecimal("1000"), stock.getSalesPrice());
     }
-    
-    @Test 
-    public void testAddNewSalesPrice() {
-        Stock stock = new Stock("AAPL", "APPLE", new BigDecimal("1000"));
+
+    @Test
+    void testGetSalesPriceZero() {
+        Stock zeroStock = new Stock("ZERO", "ZeroCorp", new BigDecimal("0"));
+        assertEquals(new BigDecimal("0"), zeroStock.getSalesPrice());
+    }
+
+    @Test
+    void testAddNewSalesPrice() {
         stock.addNewSalesPrice(new BigDecimal("1200"));
         assertEquals(new BigDecimal("1200"), stock.getSalesPrice());
     }
 
-    @Test 
-    public void testGetSalesPriceNone() {
-        Stock stock = new Stock("AAPL", "APPLE", new BigDecimal("0"));
+    @Test
+    void testAddNewSalesPriceZero() {
+        stock.addNewSalesPrice(new BigDecimal("0"));
         assertEquals(new BigDecimal("0"), stock.getSalesPrice());
     }
 
-    @Test 
-    public void testAddNewSalesPriceNone() {
-        Stock stock = new Stock("AAPL", "APPLE", new BigDecimal("1000"));
-        stock.addNewSalesPrice(new BigDecimal("0"));
-        assertEquals(new BigDecimal("0"), stock.getSalesPrice());
+    @Test
+    void testGetHistoricalPricesInitial() {
+        List<BigDecimal> history = stock.getHistoricalPrices();
+        assertEquals(1, history.size());
+        assertEquals(new BigDecimal("1000"), history.get(0));
+    }
+
+    @Test
+    void testGetHistoricalPricesAfterUpdates() {
+        stock.addNewSalesPrice(new BigDecimal("1100"));
+        stock.addNewSalesPrice(new BigDecimal("1200"));
+        assertEquals(3, stock.getHistoricalPrices().size());
+    }
+
+    @Test
+    void testGetHighestPrice() {
+        stock.addNewSalesPrice(new BigDecimal("1500"));
+        stock.addNewSalesPrice(new BigDecimal("800"));
+        assertEquals(new BigDecimal("1500"), stock.getHighestPrice());
+    }
+
+    @Test
+    void testGetLowestPrice() {
+        stock.addNewSalesPrice(new BigDecimal("1500"));
+        stock.addNewSalesPrice(new BigDecimal("800"));
+        assertEquals(new BigDecimal("800"), stock.getLowestPrice());
+    }
+
+    @Test
+    void testGetLatestPriceChangePositive() {
+        stock.addNewSalesPrice(new BigDecimal("1100"));
+        assertEquals(new BigDecimal("100"), stock.getLatestPriceChange());
+    }
+
+    @Test
+    void testGetLatestPriceChangeNegative() {
+        stock.addNewSalesPrice(new BigDecimal("900"));
+        assertEquals(new BigDecimal("-100"), stock.getLatestPriceChange());
+    }
+
+    @Test
+    void testGetLatestPriceChangeOnlyOnePrice() {
+        assertEquals(BigDecimal.ZERO, stock.getLatestPriceChange());
+    }
+
+    @Test
+    void testHistoricalPricesIsDefensiveCopy() {
+        List<BigDecimal> history = stock.getHistoricalPrices();
+        history.add(new BigDecimal("9999"));
+        assertEquals(1, stock.getHistoricalPrices().size());
+    }
+
+    // ---- Negative tests ----
+
+    @Test
+    void testNullSymbolThrows() {
+        assertThrows(IllegalArgumentException.class, () ->
+            new Stock(null, "Apple", new BigDecimal("100"))
+        );
+    }
+
+    @Test
+    void testBlankSymbolThrows() {
+        assertThrows(IllegalArgumentException.class, () ->
+            new Stock("  ", "Apple", new BigDecimal("100"))
+        );
     }
 
-    
+    @Test
+    void testNullCompanyThrows() {
+        assertThrows(IllegalArgumentException.class, () ->
+            new Stock("AAPL", null, new BigDecimal("100"))
+        );
+    }
+
+    @Test
+    void testBlankCompanyThrows() {
+        assertThrows(IllegalArgumentException.class, () ->
+            new Stock("AAPL", "  ", new BigDecimal("100"))
+        );
+    }
+
+    @Test
+    void testNullInitialPriceThrows() {
+        assertThrows(IllegalArgumentException.class, () ->
+            new Stock("AAPL", "Apple", null)
+        );
+    }
+
+    @Test
+    void testNegativeInitialPriceThrows() {
+        assertThrows(IllegalArgumentException.class, () ->
+            new Stock("AAPL", "Apple", new BigDecimal("-1"))
+        );
+    }
+
+    @Test
+    void testAddNullPriceThrows() {
+        assertThrows(IllegalArgumentException.class, () ->
+            stock.addNewSalesPrice(null)
+        );
+    }
+
+    @Test
+    void testAddNegativePriceThrows() {
+        assertThrows(IllegalArgumentException.class, () ->
+            stock.addNewSalesPrice(new BigDecimal("-10"))
+        );
+    }
 }
diff --git a/target/test-classes/StockTest.class b/target/test-classes/StockTest.class
index 1a94286..0008700 100644
Binary files a/target/test-classes/StockTest.class and b/target/test-classes/StockTest.class differ